Methods for washing and protecting photographic silver images



United States Patent METHODS FOR WASHING AND PROTECTING PHOTOGRAPHICSILVER IMAGES Edwin H. Land, Cambridge, and Milton Green, Mattapan,Mass., assignors to Polaroid Corporation, Cambridge, Mass, a corporationof Delaware No Drawing. Application February 24, 1954, Serial No.412,395

9 Claims. (CI. 96-29) This invention relates to a protective environmentfor a photographic silver image and more particularly to a method forand product of washing and protecting a photographic silver image byapplying to at least one of its faces, in a thin layer, a compositioncontaining water for dissolving residual water-soluble processingreagents from the image and a plastic material for producing aprotective coating upon the image when the composition is dried.

The processes of the invention are particularly applicable to thinphotographic silver images of the type described in the copendingapplication of Edwin H. Land, Serial No. 302,746, filed August 5, 1952for Method of Improving the Stabilization of Finished PhotographicPrints by Applying a Liquid Composition Thereto (now Patent No.2,719,791). Such a thin photographic print, for example, may be producedby applying a photographic composition, which includes a silver halidedeveloper and a silver halide solvent, to a photoexposed silver halideelement and an image-receptive element which are in superposed relation.The composition acts to reduce exposed silver halide to silver, to reactwith unreduced silver halide to form a water-soluble complex silversalt, and to transfer the salt to the image-receptive element where itis reduced to silver.

Such a thin photographic silver image ordinarily retains traces of thephotographic reagents with which it has been processed and the continuedpresence of which may adversely affect its stability. For example,silver may be oxidized by sulphur from the residue of sodium thiosulfatewhich has been employed as the solvent. Also, silver may be oxidized bysuch agents as hydrogen sulfide, often present in the atmosphere.Furthermore, traces of unexposed developer, if oxidized by atmosphericoxygen, may slightly discolor the highlights of the image.

Objects of this invention are: to provide a photographic silver imagewith a protective environment primarily containing hydrolyzed gelatin;to provide, in a novel process for washing and protecting a thinphotographic silver image of the foregoing type, the step of applying toat least one of its faces in a layer a composition comprising an aqueoussolution of hydrolyzed gelatin and the step of drying the layer toproduce a residue composed primarily of hydrolyzed gelatin; and toprovide, as novel products, protected photographic silver imagesproduced by such a process.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the several steps and the relationand order of one or more of such steps with respect to each of theothers which are exemplified in the following detailed disclosure, andthe scope of the application of which will be indicated in the claims.

A preferred composition, to be employed in accordance with the presentinvention, is an aqueous solution of a hydrolyzed gelatin havingpolypeptide chains on the average of not less than 4 and not more than12 amino acid units. Preferably, the hydrolyzed gelatin is not less than15% and not more than 40% by total weight of the solution. Such asolution, unlike a dispersion of ordinary gelatin, is fluid enough atordinary temperatures to be readily spread upon an image of theforegoing type and, when dried, provides the image with a hydrolyzedgelatin environment unexpectedly possessing protective properties forsilver similar to those of ordinary gelatin.

in general. such a solution may be prepared by hydrolyzing either alkalior acid extracted gelatin with a proteolytic enzyme such as papain,pepsin or trypsin and, when a desired degree of hydrolysis is reached,by stabilizing the solution with a preservative such as methyl p-hydroxybenzoate, cetyl pyridinium chloride or oxyquinoline.

Photographic materials useful in the production of photographic silverimages of the general type referred to above are described in detail inPatent No. 2,543,181, which issued on February 27, 1951 in the name ofEdwin H. Land for Photographic Product Comprising a Rupturahle ContainerCarrying a Photographic Processing Liquid. In a typical processemploying such materials, a viscous processing composition, containing asilver halide developer, a silver halide solvent and an alkali, isspread in a uniformly thin layer between the superposed surfaces of aphotoexposed gelatino silver halide layer and an image-receptiveelement, for example, by advancing the elements between a pair ofpressure-applying rollers. The elements are maintained in superposedrelation for a predetermined period, ordinarily of the order of 40 toseconds, during which exposed silver halide is reduced to silver andunreduced silver halide forms a water-soluble complex salt whichdilfuses through the layer of composition to the image-receptiveelement, there, upon being reduced to silver, to form a visible print.At the end of this period, the silver halide element, preferably,together with the layer of processing composition, is stripped from theimage-receptive element. Various techniques for causing the layer ofprocessing composition to adhere to the silver halide element inpreference to the image-receptive element are described in Patent No.2,647,056, issued to Edwin H. Land on July 28, 1953 for One StepPhotographic Transfer Process.

The gelatino silver halide element employed in the foregoing process,for example, is laminated to a conventional support composed of asuitable paper or a suitable plastic material such as cellulose nitrateor one of the organic acid cellulose esters including cellulose acetate,cellulose triacetate, cellulose propionate, cellulose butyrate andcellulose acetate butyrate. The image-receptive element, in the form ofa layer, of the order of 1 micron thick, upon a support of the foregoingtype, preferably includes certain materials the presence of which,during the transfer process, has a desirable effect on the amount andcharacter of silver precipitated on the image-receptive element. Animage composed of dense aggregates of silver may be formed in this layerby the process described above. As examples of silver precipitatingmaterials, mention may be made of metallic sulfides and selenides,certain colloidal metals such as colloidal silver, thiooxalates andthioacetamides. A preferred image-receptive element in which thesesilver precipitating materials are distributed is a macroscopicallycontinuous film consisting of submacroscopic agglomerates of minuteparticles of a suitable water-insoluble, inorganic, preferablysiliceous, material such as silica aerogel. Materials of the foregoingtypes are more specifically described in copending U. S. patentapplication Serial No. 727,385, filed by Edwin H. Land on February 8,1947 (now Patent No. 2,698,245) and Serial No. 164,908, now abandonedand replaced by application Serial No. 449,995, filed August 16, 1954and issued as Patent No. 2,698,237.

Preferably. there is interposed between the imagereceptive element andits support a water-impermeable layer capable of preventing thepenetration of moisture from the processing composition into thesupport. This layer is responsible for the production of a substantiallydry image only shortly after the photosensitive element is stripped fromit. This layer cooperates with a protective coating of the typedescribed above to completely envelop the image within a barrier againstagents capable of harming the image. The water-impermeable layer, forexample, may be composed of unplasticized polymethacrylic acid or one ofthe cellulosic esters such as cellulose nitrate, cellulose acetate,cellulose butyrate, cellulose propionate, cellulose acetate butyratc orcellulose acetate propionate. Preferred, however, are such rubberypolymers as polyvinyl butyral. If the support is water impermeable, ofcourse, a discrete water-impermeable layer need not be provided.

Preferably, the composition is applied to one face oi the image by meansof an absorbent applicator composed, for example, of flannel, cottonbatting or cellulose sponge which is charged with the composition. Whenthe face of the image is swabbed with such an applicator, residualreagents of the image are dissolved in the composition and, for the mostpart, transferred into the applicator and the image becomes coated witha thin layer of the composition. The composition layer is then dried toform a protective coating.

A specific example of a solution useful in accordance with the presentinvention follows:

To a dispersion of 44 pounds of 100 Bloom, alkali pretreated gelatin in19 gallons of water was added a dispersion of one-half pound of papainin one quart of water. The resulting mixture at 60 C. was stirred for aperiod of from 12 to 15 minutes during which hydrolysis of the gelatinoccurred. At the end of this period, in order to halt the hydrolysis,one quart of 7% hydrogen peroxide was added and the temperature raisedas rapidly as possible to 95 C. After the solution was filtered andcooled, one-half pound of methyl paracept was added as a preservative.The resulting solution contained, by total weight, approximately 22% ofhydrolyzed gelatin having polypeptide chains on the average ofapproximately 7 amino acid units. This solution, after being swabbed bymeans of an absorbent applicator onto a thin photographic silver imageof the above-described type, rapidly dried under ordinary atmosphericconditions to form a coating having excellent protective properties forthe image.

Since certain changes may be made in the above process without departingfrom the scope of the invention herein involved, it is intended that allmatter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

What is claimed is:

l. A method of forming a stable photographic print, said methodcomprising the steps of spreading between a gelatin-freesilver-receptive stratum and an exposed gelatino silver halide stratum,in a layer, an alkaline aqueous solution of a silver halide developerand a silver halide solvent whereby exposed silver halide is reduced tosilver and unreduced silver halide forms a water-soluble, complex silversalt which diffuses through the layer of solution to thesilver-receptive stratum where, upon being reduced to silver, it forms avisible print, stripping said print from said gelatino silver halidestratum, said print containing a residue of said solution, swabbing saidprint with an absorbent applicator charged with an alkaline aqueoussolution of hydrolyzed gelatin in order to wash said residue from saidprint into said applicator, and drying solution retained on said printin order to intimately associate said hydrolyzed gelatin with saidsilver in said print.

2. The method of claim 1 wherein said hydrolyzed gelatin has polypeptidechains on the average of not less than 4 and not more than 12 amino acidunits.

3. The method of claim 1 wherein said solution, by total weight,contains not less than 15% and not more than 40% of said hydrolyzedgelatin.

4. The method of claim 1 wherein said hydrolyzed gelatin has polypeptidechains on the average of not less than 4 and not more than 12 amino acidunits and by total weight is not less than 15% and not more than 40% ofsaid solution.

5. A method of forming a stable photographic print, said methodcomprising the steps of subjecting a gelatin free, silver-receptivestratum and an exposed gelatino silver halide stratum, in a layer, to analkaline aqueous solution of a silver halide developer and a silverhalide solvent whereby exposed silver halide is reduced to silver andunreduced silver halide forms a water-soluble, complex silver salt whichdiltuses through the layer of solution to the silver-receptive stratumwhere, upon being reduced to silver, it forms a visible print, strippingsaid print from said gelatino silver halide stratum, said printcontaining a residue of said solution, swabbing said print with anabsorbent applicator charged with an alkaline aqueous solution ofhydrolyzed gelatin in order to wash said residue from said print intosaid applicator, and drying solution retained on said print in order tointimately associate said hydrolyzed gelatin with said silver in saidprint.

6. A method of forming a stable photographic print in a gelatin-free,silver-receptive stratum, said method comprising the steps of subjectingan exposed gelatino silver halide stratum to an alkaline aqueoussolution of a silver halide developer and of a silver halide solvent,whereby exposed silver halide is reduced to silver and unreduced silverhalide forms a water-soluble silver complex, diffusing said complex fromsaid silver halide straturn to said silver-receptive stratum where, uponbeing reduced to silver, it forms a visible print, separating said printfrom said gelatino silver halide stratum, said print containing aresidue of said solution, and applying to said print an alkaline aqueoussolution of hydrolyzed gelatin in order to wash said residue from saidprint and to intimately associate said hydrolyzed gelatin with saidsilver in said print.

7. The process of claim 6 wherein said silver-receptive stratum issiliceous.

8. The process of claim 6 wherein said hydrolyzed gelatin haspolypeptide chains on the average of not less than 4 and not more than12 amino acid units.

9. The process of claim 6 wherein said aqueous solution of hydrolyzedgelatin contains not less than 15% and not more than 40% of saidhydrolyzed gelatin.

References Cited in the file of this patent UNITED STATES PATENTS1,543,301 Stock June 23, 1925 2,089,460 Wilmanns et al. Aug. 10, 19372,173,480 lung Sept. 19, 1939 2,719,791 Land Oct. 4, 1955

1. A FABRIC TESTING APPARATUS FOR DETERMINING QUALITY CHARACTERISTICS OFFABRIC AND OTHER FLEXIBLE MATERIALS COMPRISING, IN COMBINATION ARELATIVELY SMALL CLOSED TEST CHAMBER CONSISTING OF A GENERALLYCYLINDRICAL INNER WALL EXTENDING BETWEEN A PAIR OF SPACED APART ENDWALLS WITH AT LEAST ONE SAID WALLS MOVEABLE TO AFFORD ACCESS TO SAIDTEST CHAMBER; AN ELECTRIC MOTOR MOUNTED ADJACENT SAID TEST CHAMBER WITHA ROTATABLE SHAFT DRIVEN BY SAID MOTOR EXTENDING THROUGHT ONE OF THEAFOREMENTIONED END WALLS INTO SAID TEST CHAMBER, AND MEANS FOR DRIVING ASAMPLE OF MATERIAL WITHIN SAID CONTAINER IN A RANDOM, ZIG-ZAG PATH OFMOVEMENT ALONG A GENERALLY CIRCULAR ORBIT AND SIMULTANEOUSLY CAUSING ITTO REPEATEDLY IMPINGE THE WALLS OF SAID CONTAINER AND CAROM THEREFROMWHEREBY SAID SAMPLE IS SUBJECTED TO BOTH INTERNAL AND EXTERNAL FRICTIONAS IT PROGRESSES; SAID MEANS CONSISTING OF A ROTARY IMPELLER HAVING AHUB PORTION CENTRALLY DISPOSED ON THE AXIS OF SAID CONTAINER AND ATLEAST ONE PAIR OF FLAT PADDLES, EACH PADDLE EXTENDING FROM SAID HUB TO APOINT ADJACENT THE CYLINDRICAL WALL OF THE CONTAINER AND BETWEEN THE ENDWALLS THEREOF, THE PADDLES OF SAID PAIR BEING INCLINED TO SAID HUB ANDLYING IN SUBSTASNTIALLY THE SAME PLANE. SOLUTION OF A SILVER HALIDEDEVELOPER AND A SILVER HALIDE SOLVENT WHEREBY EXPOSED SILVER HALIDE ISREDUCED TO SILVER AND UNREDUCED SILVER HALIDE FORMS A WATER-SOLUBLE,COMPLEX SILVER SALT WHICH DIFFUSES THROUGH THE LAYER OF SOLUTION TO THESILVER-RECEPTIVE STRATUM WHERE, UPON BEING REDUCED TO SILVER, IT FORMS AVISIBLE PRINT, STRIPPING SAID PRINT FROM SAID GELATINO SILVER HALIDESTRATUM, SAID PRINT CONTAINING A RESIDUE OF SAID SOLUTION, SWABBING SAIDPRINT WITH AN ABSORBENT APPLICATOR CHARGED WITH AN ALKALINE AQUEOUSSOLUTION OF HYDROLYZED GELATIN IN ORDER TO WASH SAID RESIDUE FROM SAIDPRINT INTO SAID APPLICATON, AND DRYING SOLUTION RETAINED ON SAID PRINTIN ORDER TO INTIMATELY ASSOCIATE SAID HYDROLYZED GELATIN WITH SAIDSILVER IN SAID PRINT.